1. Field of the Invention
The present invention relates to new ether and ester group-containing polyhydroxyl compounds, which are produced by esterifying polyether polyols with monocarboxylic acids, and their use as polyol component in the production of polyurethane plastics materials, particularly in two-component polyurethane coating agents or polyurethane casting compositions.
2. Description of the Prior Art
Coating agents and casting compositions containing mixtures as binders which react to completion to form polyurethanes are known (c.f. e.g. Wagner Sarx, Lackkunstharze, 5th Edition, Carl Hanser Verlag, Munich, 1971, page 153 to 173 and Kunststoffhandbuch, Volume 7, Hanser Verlag 1983, page 540 to 561, and pages 425-428).
On pages 169 to 170 of the first mentioned publication and on pages 556 to 559 of the second mentioned publication, solvent-free systems are also described which allow coatings with a desired thickness to be produced in a working process. The solvent-free coating agents have become particularly interesting in connection with the stricter environmental regulations. Low viscosity starting materials are necessary for the production of solvent-free coatings. Polyisocyanate mixtures of the diphenyl methane series are generally used as the polyisocyanate component (mixtures of 4,4'-diisocyanatodiphenyl methane and optionally 2,4'-diisocyanatodiphenyl methane with varying quantities of higher functional homologues, as are obtained by the phosgenation of aniline/formaldehyde condensation products). However, difficulties occur in the selection of the polyol component. The available hydroxyl group-containing polyester polyols provide good mechanical properties after cross-linking the polyisocyanates, but have deficiencies with respect to stability to hydrolysis. Furthermore, the hydroxyl group-containing polyester polyols are highly viscous due to their chemical constitution, which is a disadvantage for the production of solvent-free systems. The known hydroxyl group-containing polyether polyols often have a sufficiently low viscosity and are also resistant to hydrolytic influences, but result in polyurethanes having mechanical properties which are clearly inferior to the polyester urethanes. Moreover, the known polyether polyols are not well suited for reaction with polyisocyanates in coatings since they have a tendency to form bubbles.
Various proposals have been made for the elimination of the disturbing formation of bubbles. Alkali-aluminosilicates with a zeolite structure which are activated in solvent-free polyurethane coatings and serve to bind the disturbing moisture, are often used. These synthetically produced alkali-aluminosilicates have become known as molecular sieves. However, in spite of the use of molecular sieve zeolites, processing, particularly with high air moisture, often results in the damaging formation of foam, especially when using pure polyether polyols.
It is thus an object of the present invention to provide new polyhydroxyl compounds which do not suffer from the above disadvantages, have a viscosity which is sufficiently low for two-component polyurethane systems which are solvent-free or have a low solvent content, have good compatibility with the reaction partners (polyisocyanates), are suitable as a binder component for two-component polyurethane coating agents or polyurethane casting compositions and can be processed to form bubble-free end products with good mechanical properties.
This object may be achieved by the preparation of the polyhydroxyl compounds according to the invention described in more detail below.